Because liquid crystal displays have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, liquid crystal displays are considered by many to have the potential to completely replace cathode ray tube (CRT) monitors and televisions.
Referring to FIG. 1, a typical liquid crystal display 3 is shown. The liquid crystal display 3 includes a liquid crystal panel 30 and a backlight module 39 adjacent to the liquid crystal panel 30. The liquid crystal panel 30 includes a first substrate assembly 31, a second substrate assembly 32 parallel to the first substrate assembly 31, a liquid crystal layer 33 sandwiched between the first substrate assembly 31 and the second substrate assembly 32.
Referring to FIG. 12, the first substrate assembly 31 includes a plurality of parallel strip-shaped common electrodes 310 at an inner surface thereof, which are made from indium tin oxide (ITO). Odd-numbered common electrodes 310 are electrically connected with a first common electrode bus line 311. Even-numbered common electrodes 310 are electrically connected with a second common electrode bus line 312.
Referring to FIG. 13, the second substrate assembly 32 includes a number 2n (where n is a natural number) of scanning lines 321 that are parallel to each other and that each extend along a first direction, and a number k (where k is also a natural number) of signal lines 322 that are parallel to each other and that each extend along a second direction orthogonal to the first direction, a number 2n of common electrode lines 325 that are parallel to each other and that each extend along the first direction, and a plurality of thin film transistors (TFTs) 323 that function as switching elements. Each thin film transistor 323 is provided in the vicinity of a respective point of intersection of the scanning lines 321 and the signal lines 322. The second substrate assembly 32 further includes a plurality of pixel electrodes 324 formed on a surface thereof facing the first substrate assembly 32.
Each thin film transistor 323 includes a gate electrode (not labeled), a source electrode (not labeled), and a drain electrode (not labeled). The gate electrode of each thin film transistor 323 is connected with a corresponding scanning line 321. The source electrode of each thin film transistor 323 is connected with a corresponding signal line 322. The drain electrode of each thin film transistor 323 is connected to a corresponding pixel electrode 324.
The scanning lines 321 are connected with a scanning line driving circuit 326 for receiving scanning signals. The signal lines 322 are connected with a signal line driving circuit 327 for receiving gradation voltages. The common electrode lines 325 are connected to a common voltage generating circuit 328. The common voltage generating circuit 328 is configured for generating a first common voltage and a second common voltage to the common electrode lines 325 of the second substrate assembly 32 and the common electrodes 310 of the first substrate assembly 31. The scanning line driving circuit 326, the signal line driving circuit 327 and the common voltage generating circuit 328 are connected with a timing control circuit 329 in order to work in a predetermined sequence.
The pixel electrodes 324, the common electrodes 310 facing the pixel electrodes 324, and the liquid crystal layer 33 sandwiched between the pixel and common electrodes 324, 310 cooperatively define a plurality of pixel units (not labeled). Each pixel unit includes a liquid crystal capacitor Clc and a storage capacitor Cs. The liquid crystal capacitor Clc and the storage capacitor Cs are both electrically connected with the common electrodes 310. A common voltage of each common electrode 310 and a gradation voltage of the corresponding pixel electrode 324 cooperatively define a display voltage, which is used to control an amount of light transmission at the corresponding pixel unit. The display voltage keeps in a frame period.
Referring to FIG. 14, an abbreviated waveform diagram of driving signals of the liquid crystal display 3 is shown. Scanning signals G1-G2n are generated by the scanning line driving circuit 326, and are applied to the scanning lines 321. Gradation voltages (Vn) are generated by the signal line driving circuit 327, and are sequentially applied to the signal lines 322. A common voltage (Vcom1) is applied to odd-numbered common electrodes 310. A common voltage (Vcom2) is applied to even-numbered common electrodes 310. Even-numbered common electrodes 310 and odd-numbered common electrodes 310 are respectively provided voltages having opposite polarities and a constant potential in each frame period. And, the polarities of even-numbered common electrodes 310 and odd-numbered common electrodes 310 are respectively alternated in a next frame period. Only one scanning signal pulse is applied to each scanning line 321 during each frame period, the scanning signal pulse having a duration which is equal to a period of clock pulses of a scanning clock signal. The scanning signal pulses are output sequentially to the scanning lines 321 to activate the thin film transistors 323 connected to the scanning lines 321.
During Frame 1, when an odd-numbered scanning line 321 is scanned, the signal line driving circuit 327 outputs first gradation voltages corresponding to image data to the signal lines 322. Then the first gradation voltages are applied to the pixel electrodes 324 via the activated thin film transistors 323. A corresponding odd-numbered common electrodes 310 is provided with the first common voltage. The first common voltage has a positive polarity, and is greater than the first gradation voltages. Thus, the display voltages of corresponding pixel units have negative polarities.
When an even-numbered scanning line 321 is scanned, the signal line driving circuit 327 outputs second gradation voltages corresponding to image data to the signal lines 322. Then the second gradation voltages are applied to the pixel electrodes 324 via the activated TFTs 323. A corresponding even-numbered common electrode 310 is provided with the second common voltage. The second common voltage has a negative polarity, and is less than the second gradation voltages. Thus, the display voltages of corresponding pixel units have positive polarities. FIG. 15 (a) shows the polarities of the display voltages of the pixel units in Frame 1.
During Frame 2, when odd-numbered scanning line 321 is scanned, the signal line driving circuit 327 outputs second gradation voltages to the corresponding pixel electrodes 324 via the activated TFTs 323. The corresponding odd-numbered common electrode 310 is applied with a second common voltage. The second common voltage has a negative polarity, and is less than the second gradation voltages. Thus, the display voltages have positive polarities.
When even-numbered scanning line 321 is scanned, the signal line driving circuit 327 outputs first gradation voltages to the corresponding pixel electrodes 324 via the activated TFTs 323. The corresponding even-numbered common electrode 310 is applied with a first common voltage. The first common voltage has a positive polarity, and is greater than the first gradation voltages. Thus, the display voltages of corresponding pixel units have negative polarities. FIG. 15 (b) shows the polarities of the display voltages of the pixel units in Frame 2.
The pixel units connected with the same scanning lines 321 have the same polarities of the display voltages, the pixel units in an adjacent scanning line 321 have the alternated polarities of the display voltages, and the polarities of the display voltages of the pixel units are alternated in a next frame period. As a result, a row inversion mode is realized.
However, the liquid crystal capacitors Clc and the storage capacitors Cs are both electrically connected with the common electrodes 310. During a period between every continuous two frame periods, the voltages of odd-numbered common electrodes 310 and even-numbered common electrodes 310 are respectively alternated. Thus the liquid crystal capacitors Clc and the storage capacitors Cs need to be discharged reversely. Therefore, a power consuming of the liquid crystal display 3 is great.
What is needed, therefore, is a liquid crystal display that can overcome the above-described deficiencies. What is also needed, is a driving method of such liquid crystal display.